analyzing-packed-malware-with-upx-unpacker
Identifies and unpacks UPX-packed and other packed malware samples to expose the original executable code for static analysis. Covers both standard UPX unpacking and handling modified UPX headers that prevent automated decompression. Activates for requests involving malware unpacking, UPX decompression, packer removal, or preparing packed samples for analysis.
84
81%
Does it follow best practices?
Impact
Pending
No eval scenarios have been run
Passed
No known issues
Quality
Discovery
100%Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.
This is an excellent skill description that clearly defines a specialized niche (UPX/packer removal for malware analysis), lists concrete capabilities including edge cases (modified UPX headers), and provides explicit trigger conditions. The description is concise, uses third person voice throughout, and includes natural keywords that a malware analyst would use.
| Dimension | Reasoning | Score |
|---|---|---|
Specificity | Lists multiple specific concrete actions: identifies packed samples, unpacks UPX-packed malware, handles modified UPX headers, exposes original executable code for static analysis. These are concrete, well-defined capabilities. | 3 / 3 |
Completeness | Clearly answers both 'what' (identifies and unpacks UPX-packed and other packed malware, handles modified UPX headers) and 'when' ('Activates for requests involving malware unpacking, UPX decompression, packer removal, or preparing packed samples for analysis'). | 3 / 3 |
Trigger Term Quality | Includes strong natural keywords users would say: 'UPX', 'packed malware', 'unpacking', 'UPX decompression', 'packer removal', 'packed samples', 'static analysis', 'modified UPX headers'. Good coverage of terms a reverse engineer would naturally use. | 3 / 3 |
Distinctiveness Conflict Risk | Highly distinctive niche focusing specifically on UPX packing/unpacking in malware analysis context. Very unlikely to conflict with other skills given the specialized domain of malware unpacking and packer removal. | 3 / 3 |
Total | 12 / 12 Passed |
Implementation
62%Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.
The skill provides excellent actionable guidance with executable code and a well-structured multi-step workflow with validation checkpoints and fallback paths. However, it is significantly bloated with redundant sections (Key Concepts glossary, Tools & Systems descriptions, Common Scenarios that restate the workflow) that explain things Claude already knows. Trimming the glossary, tool descriptions, and redundant scenario would cut the skill nearly in half without losing any actionable value.
Suggestions
Remove the 'Key Concepts' glossary table entirely — Claude already knows what packing, OEP, PUSHAD/POPAD, entropy, and magic bytes are.
Remove or drastically condense the 'Tools & Systems' section since all tools are already listed in Prerequisites with sufficient context.
Merge the 'Common Scenarios' section into the main workflow as brief inline notes (e.g., pitfalls as warnings at relevant steps) rather than restating the entire workflow.
Consider splitting the Output Format template and the manual debugger unpacking instructions into separate referenced files to improve progressive disclosure.
| Dimension | Reasoning | Score |
|---|---|---|
Conciseness | The skill is excessively verbose at ~250+ lines. The 'Key Concepts' glossary table explains terms Claude already knows (what packing is, what PUSHAD/POPAD does, what entropy means). The 'Tools & Systems' section redundantly describes tools already mentioned in Prerequisites. The 'Common Scenarios' section largely restates the workflow steps. The 'When to Use' and 'Do not use' sections, while useful, add bulk that could be condensed. | 1 / 3 |
Actionability | The skill provides fully executable bash commands and Python scripts throughout. The pefile-based entropy analysis, UPX header repair script, and validation scripts are all copy-paste ready with concrete code. The manual unpacking steps with x64dbg are specific and procedural. | 3 / 3 |
Workflow Clarity | The 5-step workflow is clearly sequenced with explicit validation in Step 5. There are clear fallback paths (Step 2 fails → Step 3 header repair → Step 4 manual unpacking). The validation step checks entropy, imports, and file sizes to confirm successful unpacking. | 3 / 3 |
Progressive Disclosure | The content is monolithic — everything is in a single file with no references to external documents. The Key Concepts table, Tools & Systems section, Common Scenarios, and Output Format template could all be split into separate reference files. However, the content is at least organized with clear section headers. | 2 / 3 |
Total | 9 / 12 Passed |
Validation
90%Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.
Validation — 10 / 11 Passed
Validation for skill structure
| Criteria | Description | Result |
|---|---|---|
frontmatter_unknown_keys | Unknown frontmatter key(s) found; consider removing or moving to metadata | Warning |
Total | 10 / 11 Passed | |
- Repository
- mukul975/Anthropic-Cybersecurity-Skills
- Commit
888bbe4
- Reviewed
Table of Contents
Is this your skill?
If you maintain this skill, you can claim it as your own. Once claimed, you can manage eval scenarios, bundle related skills, attach documentation or rules, and ensure cross-agent compatibility.